Patterning process and chemical amplified photoresist composition

ABSTRACT

A lithography method includes forming a photosensitive layer on a substrate, exposing the photosensitive layer, baking the photosensitive layer, and developing the exposed photosensitive layer. The photosensitive layer includes a polymer that turns soluble to a base solution in response to reaction with acid, a plurality of photo-acid generators (PAGs) that decompose to form acid in response to radiation energy, and a plurality of quenchers having boiling points distributed between about 200 C and about 350 C. The quenchers also have molecular weights distributed between 300 Dalton and about 20000 Dalton, and are vertically distributed in the photosensitive layer such that a first concentration C1 at a top portion of the photosensitive layer is greater than a second concentration C2 at a bottom portion of the photosensitive layer.

CROSS REFERENCE

This application claims the benefit of U.S. Provisional Application61/254,305 entitled “Patterning Process and Chemical AmplifiedPhotoresist Composition,” filed Oct. 23, 2009, herein incorporated byreference in its entirety.

BACKGROUND

Semiconductor technologies are continually progressing to smallerfeature sizes, down to 65 nanometers, 45 nanometers, and below. Apatterned photoresist layer used to produce such small feature sizestypically has a high aspect ratio. Maintaining a desired criticaldimension (CD) can be very difficult for various reasons. For example,when a chemical amplified photoresist layer is used, the patternedphotoresist layer can have a top rounding profile.

SUMMARY

The present disclosure describes a lithography method, photolithographymaterial, and a device produced by such method and products. In oneembodiment, the method includes forming a photosensitive layer on asubstrate, exposing the photosensitive layer, baking the photosensitivelayer, and developing the exposed photosensitive layer. Thephotosensitive layer includes a polymer that turns soluble to a basesolution in response to reaction with acid, a plurality of photo-acidgenerators (PAGs) that decompose to form acid in response to radiationenergy, and a plurality of quenchers having boiling points distributedbetween about 20° C. and about 35° C. The quenchers also have molecularweights distributed between 300 Dalton and about 20000 Dalton, and arevertically distributed in the photosensitive layer such that a firstconcentration C1 at a top portion of the photosensitive layer is greaterthan a second concentration C2 at a bottom portion of the photosensitivelayer.

In another embodiment, a method for a lithography process includesforming a first photosensitive layer on a substrate, forming a secondphotosensitive layer on the first photosensitive layer, and performingan exposing process to the first and second photosensitive layers. Thefirst photosensitive layer includes a first photo-acid generator (PAG)distributed in the first photosensitive layer, and a first quenchersdistributed in the first photosensitive layer and having a firstconcentration. The second photosensitive layer includes a second PAGdistributed in the second photosensitive layer, and a second quenchersdistributed in the second photosensitive layer and having a secondconcentration greater than the first concentration.

In another embodiment, a method for lithography patterning includesforming a first photosensitive layer on a substrate, the firstphotosensitive layer including a first photo-acid generator (PAG) of afirst concentration. The method further includes forming a secondphotosensitive layer on the first photosensitive layer, the secondphotosensitive layer including a second PAG of a second concentrationless than the first concentration. An exposing process can then beperformed on the first and second photosensitive layers.

In one embodiment, a photosensitive material includes a polymer thatturns soluble to a base solution in response to reaction with acid, aplurality of photo-acid generators (PAGs) that decompose to form acid inresponse to radiation energy, and a plurality of quenchers having aboiling point greater than about 300 C.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1 a through 1 c illustrate sectional views of one exemplarysemiconductor device having a photosensitive layer being exposed duringa lithography process.

FIGS. 2 a through 2 c illustrate sectional views of semiconductor devicehaving a photosensitive layer at various stages of a lithography processconstructed according to aspects of the present disclosure in oneembodiment.

FIGS. 3 a through 3 c illustrate sectional views of semiconductor devicehaving a photosensitive layer at various stages of a lithography processconstructed according to aspects of the present disclosure in anotherembodiment.

FIGS. 4 a and 4 b illustrate various embodiments of a photosensitivematerial having high boiling-point quencher.

FIG. 5 illustrate sectional views of a semiconductor device having aphotosensitive layer at various stages of a lithography processconstructed according to aspects of the present disclosure.

FIG. 6 illustrate sectional views of a semiconductor device having aphotosensitive layer at various stages of a lithography processconstructed according to aspects of the present disclosure.

FIG. 7 illustrate sectional views of a semiconductor device having aphotosensitive layer at various stages of a lithography processconstructed according to aspects of the present disclosure.

FIG. 8 provides a table of comparison among various photosensitivematerials according to various embodiments.

FIG. 9 provides a table of comparison among various photosensitivematerials according to various embodiments.

FIG. 10 is a flowchart of a method for immersion photolithographypatterning constructed according aspects of the present disclosure inone embodiment.

FIGS. 11 a through lid illustrate sectional views of a semiconductordevice at various stages of a lithography process constructed accordingto aspects of the present disclosure.

FIG. 12 is a flowchart of a method for immersion photolithographypatterning constructed according aspects of the present disclosure inanother embodiment.

FIGS. 13 a through 13 d illustrate sectional views of a semiconductordevice at various stages of a lithography process constructed accordingto aspects of the present disclosure.

DETAILED DESCRIPTION

It is understood that the following disclosure provides many differentembodiments, or examples, for implementing different features of variousembodiments. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Forexample, the formation of a first feature over or on a second feature inthe description that follows may include embodiments in which the firstand second features are formed in direct contact, and may also includeembodiments in which additional features may be formed interposing thefirst and second features, such that the first and second features maynot be in direct contact. In addition, the present disclosure may repeatreference numerals and/or letters in the various examples. Thisrepetition is for the purpose of simplicity and clarity and does not initself dictate a relationship between the various embodiments and/orconfigurations discussed.

FIGS. 1 a through 1 c provide sectional views of a semiconductor device50 at various lithography processing steps. In a current lithographyprocess for patterning a substrate 52, a photoresist layer 54 is coatedon the substrate 52 as shown in FIG. 1 a; then an ultraviolet (UV) beamis applied to the photoresist layer 54 during an exposure process,generating acid 56 in the exposed photoresist. However, the lightintensity decreases due to the light absorption by the photoresistcomponent (such as the photo acid generator) or topography issue,resulting in the corresponding top rich and bottom weak aciddistribution, as illustrated in FIG. 1 b. After post exposure baking(PEB) and developing by a basic solution, an opening 58 is revealed witha top rounding and/or scamming profile, as illustrated in FIG. 1 c.

FIGS. 2 a through 2 c provide sectional views of a semiconductor device100 at various lithography patterning steps. Referring to FIGS. 2 athrough 2 c, the semiconductor device 100 and the method making the sameare collectively described. The semiconductor device 100 may be asemiconductor wafer or other suitable device. In the present embodiment,the semiconductor device 100 includes a silicon substrate 102 havingvarious doped regions, dielectric features, and/or multilevelinterconnects. The substrate may alternatively include other suitablesemiconductor material, including Ge, SiGe, or GaAs. The substrate mayalternatively include a non-semiconductor material such as a glass platefor thin-film-transistor liquid crystal display (TFT-LCD) devices. Thesemiconductor device 100 may further include one or more material layersto be patterned. Additionally, disposed on the semiconductor substrate102 are other suitable material layers including organic bottom antireflecting coating (BARC), inorganic BARC, etch resistance organiclayer, and/or adhesion enhancement organic layer.

A photosensitive material layer (or photosensitive layer, photoresistlayer or resist layer) 104 is disposed on the substrate 102. Forexample, a spin-coating technique is utilized to form the photosensitivelayer 104 on the substrate 102. In the present embodiment, thephotosensitive layer 104 has a thickness ranging between about 500angstroms and about 5000 angstroms. In another embodiment, thephotosensitive layer 104 may have a thickness ranging between about 1000angstroms and 2000 angstroms. The photosensitive layer 104 utilizes achemical amplification (CA) resist material. In one embodiment, apositive CA resist material includes a polymer material that turnssoluble to a developer such as a base solution after the polymer isreacted with acid. Alternatively, the CA resist material can be negativeand include a polymer material that turns insoluble to a developer suchas a base solution after the polymer is reacted with acid. Thephotosensitive layer 104 further includes a solvent filling inside thepolymer. The solvent may be partially evaporated by a soft bakingprocess. The photosensitive layer 104 also includes photo-acid generator(PAG) distributed in the photosensitive layer. When absorbing photoenergy, the PAG decomposes and forms a small amount of acid. The PAG mayhave a concentration ranging between about 1% and 15% wt of thephotosensitive layer 104.

The photosensitive layer 104 also includes a quencher 106 distributed inthe solvent and polymer. The quencher 106 is base type and is capable ofneutralizing acid. Collectively or alternatively, the quencher mayinhibit other active components of the photosensitive layer 104, such asinhibiting photo acid from reaction. The quencher 106 is not uniformlydistributed in the photosensitive layer 104 along a direction 108perpendicular to the photosensitive layer. Particularly, the quencher106 has a vertically graded distribution in the photosensitive layer 104such that the top concentration is greater than the bottomconcentration. In one particular embodiment, a top portion 110 of thephotosensitive layer has a thickness of about 25% of the photosensitivelayer; a bottom portion 112 of the photosensitive layer has a thicknessof about 25% of the photosensitive layer. The quencher 106 isdistributed in the top portion 110 with a first concentration C1; thequencher is distributed in the bottom portion 112 with a secondconcentration C2; and the first concentration is greater than the secondconcentration by an amount ranging between about 5% to about 30%. Inother words, (C1-C2)/C2 ranges between about 5% and about 30%. A softbaking process may be further applied to the photosensitive layer 104 toreduce the solvent in the photosensitive layer.

The semiconductor device 100 is then moved to a lithography apparatusfor an exposing process. In one embodiment, the exposing processutilizes an immersion photolithographic technique. In the exposingprocess, the photosensitive layer 104 is exposed to a radiation energysuch as deep ultra-violet (DUV) through a photomask (mask or reticle)having a predefined pattern, resulting in a resist pattern that includesa plurality of exposed regions such as exposed features 114 and aplurality of unexposed regions. The radiation energy may include a 248nm beam by Krypton Fluoride (KrF) excimer lasers or a 193 nm beam byArgon Fluoride (ArF) excimer lasers. The lithography apparatus mayfurther include an immersion fluid between the semiconductor device 100and a lens of a lithography apparatus. The immersion fluid may includede-ionized water (DI water or DIW). The fluid may further includechemical additives such as acid, salt, or polymer.

In this embodiment, the photosensitive layer 104 is positive. Throughthe interaction between the PAG and the radiation energy, acid 116 isgenerated in the exposed region 114 of the photosensitive layer 104. Asmentioned earlier, various light effects can introduce a deviation fromthe uniformly distributed acids. For example, light absorption causesthe light density to be less in the bottom of the photosensitive layer,therefore, less acid is generated there. In another example, thetopography issue (rough surface) introduces diffraction and furtherdegrades the distribution of the generated acid. In the presentdisclosure, the quencher 106 has a graded distribution in a way that theconcentration decreases from the top surface to the bottom surface ofthe photosensitive layer; the graded distribution of the quenchercompensates the light effects. Therefore, the generated acid 116 in theexposed region 114 of the photosensitive layer is uniformly distributedalong the vertical direction 108, as illustrated in FIG. 2 b.

In one embodiment, a post-exposure baking (PEB) process may be appliedto the exposed the photosensitive layer. Then a developing solution(developer) is applied to the photosensitive layer to develop theexposed photosensitive layer, forming an opening 118 with verticalprofile that is relatively free of defects (e.g., reduced top roundingand scumming profile), as illustrated in FIG. 2 c.

FIGS. 3 a through 3 d provide sectional views of a semiconductor device120 at various lithography patterning steps. The semiconductor device120 and the method making the same are collectively described withreference to these figures. The semiconductor device 120 includes asubstrate 102. A photosensitive layer 122 is coated on the substrate102. The photosensitive layer 122 utilizes a chemical amplification (CA)resist material. In one embodiment, a positive CA resist materialincludes a polymer material that turns soluble to a developer such as abase solution after the polymer is reacted with acid. The photosensitivelayer 122 further includes a solvent filling inside the polymer. Thephotosensitive layer 122 also includes PAG distributed in thephotosensitive layer. When absorbing photo energy, the PAG decomposesand forms a small amount of acid. The photosensitive layer 122 includeshigh boiling point (BP) quencher 124 distributed in the photosensitivelayer, as shown in FIG. 3 a. In one embodiment, the quencher has aboiling point ranging between about 200 C. and about 350 C. In anotherembodiment, the quencher 124 includes a molecular weight (MW) rangingbetween about 300 Dalton and about 20,000 Dalton. For example, theaverage MW ranges between about 300 Dalton and about 20,000 Dalton. Inanother embodiment, the molecular weight of the quencher is dispersedand the quencher 124 includes molecular weights distributed in a rangebetween about 300 Dalton and about 20,000 Dalton. In this case, theboiling point of the quencher 12 is distributed in a range between about200 C. and about 350 C.

The coated photosensitive layer 104 may be baked in a step, referred toas pre baking process, to reduce the solvent. During the coating processand the pre baking process, the quencher 124 is concentrated in the topportion of the photosensitive layer due to the surface energy and/orphase separation. In one example, the quencher is concentrated in a topportion by phase separation. In one embodiment, the top phase separatedportion has a thickness ranging between 10 angstrom and 3000 angstrom.In another embodiment, the top phase separated portion has a thicknessranging between 10 angstrom and 1000 angstrom.

Particularly, the quencher diffuses toward the top surface of thephotosensitive layer and is redistributed such that the concentration ofthe quencher is increased from the bottom to the top surface. Thequencher is designed to enhance the surface energy difference or phaseseparation such that the quencher will diffuse toward the top surfacebecause of one or more factors associated with the surface energydifference and phase separation. In various embodiments, these factorsinclude, molecular weight difference, polarity difference,hydrophilic/hydrophobic difference, solubility to solvent difference,and polymer solubility. In one example, molecular weight difference is asuch factor to introduce diffusion toward to the top surface because anadditive (such as quencher in the present example) having a lowermolecular weight can diffuse into a top region of the photosensitivelayer during a pre bake process. Another example is polarity difference.An additive having different polarity to the solvent can diffuse intothe top region of the photosensitive layer during a pre bake process.For example, if the resist material is more non polar compared to theadditive, the additive will diffuse to the top surface during or after athermal baking process. Another example is hydrophilic/hydrophobicdifference. If an additive has different hydrophilic/hydrophobic ratio,the additive will separate and diffuse during a thermal baking process.Another example is the difference of solubility to solvent. If theadditive has a solubility to the solvent higher than the backbone resistpolymer, the additive can diffuse into the top region of the resistduring a baking process. Another example is polymer solubility. If theadditive polymer and the resist polymer have different hydrogen bondingor Vander Waal force with each other, it will cause separation duringthermal baking.

After a pre baking process, the quencher 124 is redistributed with agraded distribution along the direction perpendicular to the substrate102, such as the one described in FIG. 2 a. In one embodiment, a topportion of the photosensitive layer has a thickness of about 25% of thephotosensitive layer; a bottom portion of the photosensitive layer has athickness of about 25% of the photosensitive layer; the quencher isdistributed in the top portion with a first concentration C1; thequencher is distributed in the bottom portion with a secondconcentration C2; and the first concentration is greater than the secondconcentration. In furtherance of the embodiment, (C1-C2)/C2 rangesbetween about 5% and about 30%.

The quencher used in the conventional CA photoresist has low molecularweight (such as 100˜300) and low boiling ranges (such as 100˜250 C). Thequencher in the top surface portion is evaporated from the surface, thusthe concentration of quencher is reduced in the top surface portion. Inthe present disclosure, the quencher has increased both the molecularweight and boiling temperature (or boiling point). With reference toFIG. 3 c, the surface evaporation 126 is substantially reduced oreliminated due to the high molecular weight and boiling point. Thegraded distribution of the quencher is substantially maintained, asshown in FIG. 3 d.

The semiconductor device 120 and the method making the same provide away to achieve the graded quencher concentration described in FIG. 2 ausing the quencher having high molecular weight and high boiling point.FIGS. 4 a and 4 b provide two examples of the quencher 124 having highmolecular weight and high boiling point. In one example, the quencher isa trisubstituent amine with a formula shown in FIG. 4 a, in which eachof Ra, Rb and Rc include H or alkyl groups with carbon number 6˜15. Eachof Ra, Rb and Rc may further includes a chemical group selected from the—Cl; —Br; —I; —NO2; —SO3-; —H—; —CN; —NCO, —OCN; —CO2-; —OH; —OR*,—OC(O)CR*; —SR, —SO2N(R*)2; —SO2R*; SOR; —OC(O)R*; —C(O)OR*; —C(O)R*;—Si(OR*)3; —Si(R*)3; and epoxyl groups. R* is H, an unbranched orbranched, cyclic or noncyclic, saturated or unsaturated alkyl or alkenylor alkynyl groups.

In another example, the quencher is polymeric quencher with a formulashown in FIG. 4 b. In the formula, R1˜R5 are H, F, alkyl, andfluoroalkyl groups with carbon number equal or less than 3. Ra˜Rd and Rfare linking groups, and which comprise at least one of the —CO—;—C(═O)O—; —S—; —P—; —P(O2)-; —C(═O)S—; —O—; —N—; —C(═O)N—; —SO2O—;—SO2S—; —SO—, and —SO2-. R6˜R11 and Rz are straight, branched or cylclicalky, fluoro alkyl, alkoxyl, and fluoro alkoxyl chain with carbon numberfrom 1˜15 and may further include one of —Cl; —Br; —I; —NO2; —SO3-; —H—;—CN; —NCO, —OCN; —CO2-; —OH; —OR*, —OC(O)CR*; —SR, —SO2N(R*)2; —SO2R*;SOR; —OC(O)R*; —C(O)OR*; —C(O)R*; —Si(OR*)3; —Si(R*)3; epoxyl groups,and combinations thereof. R* is H, an unbranched or branched, cyclic ornoncyclic, saturated or unsaturated alkyl or alkenyl or alkynyl groups.The parameter ‘x’ is between 1˜20. The above polymeric quencher has amolecular weight distributed in a range between 1000 and 20000 Daltons.

The differences between the conventional quencher and the disclosedquencher, and the advantages of the disclosed quencher are furtherexplained in one example below with reference to FIG. 5 and FIG. 6. FIG.5 are sectional views of the conventional photoresist 54 in variousprocessing stages. Referring to FIG. 5, a conventional quencher 127 hasa molecular weight less than 300 Daltons. When an immersion lithographyprocess is implemented, the strong interaction between the immersionliquid, such as water drop 128, will lead to leaching of the quencher tothe water or quencher aggregation with non-uniform horizontaldistribution of the quencher. The leaching reduces the concentration ofthe quencher in the top surface portion. The aggregation degrades thecritical dimension uniformity (CDU). In one example of forming contactholes using the conventional photoresist, some contact holes are missing(blind) due to the CDU degradation.

FIG. 6 provides a photosensitive layer 122 incorporated with a polymericquencher 129 having molecular weight greater than 1000 Daltons accordingto various aspects of the present disclosure. Because of the highmolecular weight, the mobility of the quencher is substantially reduced.The leaching and aggregation are eliminated or reduced accordingly. Thehigh concentration of the quencher in the top portion of the resistlayer is maintained with a non-uniform distribution along the verticaldirection. A uniform distribution in the surface (or horizontaldirection) is maintained as well.

FIG. 7 provides one example of a surface switchable photosensitive layer(photoresist or resist) coated on a wafer and the method of using thesame in a lithography process. During the baking process, some of theswitchable polymer inside the resist film move to the surface portion ofthe resist film, and are substantially separated from the bottom normalresist polymer. The switchable polymer can increase its solubility towater after contacting to base solution (such as tetramethyl ammoniumhydroxide developing solution). After a pattern exposing process, PEB,and developing, the resist pattern is formed and the switchable polymeris substantially taken away during the developing process. Therefore,the resist top loss for the switchable resist is more than aconventional resist.

FIG. 8 provides a table of comparison among various resist materialaccording various more embodiments of the present disclosure. FIG. 9provides another table of comparison among various resist materialaccording to various embodiments of the present disclosure.

FIG. 10 provides a flowchart of a lithography method 130. FIGS. 11 athrough 11 d provide sectional views of a semiconductor device 150fabricated by the method 130 through various lithography patterningsteps, constructed according to various aspects of the presentdisclosure. Referring to FIGS. 10 and 11 a˜11 d, the method 130 and thesemiconductor device 150 are collectively described. The semiconductordevice 150 includes a substrate 152, substantially similar to thesubstrate 102 of FIG. 2.

The method 130 begins at step 132 by forming a first photosensitivelayer 154 on the substrate 152, as illustrated in FIG. 11 a. The firstphotosensitive layer 154 utilizes a chemical amplification (CA) resistmaterial. In one embodiment, a positive CA resist material includes apolymer material that turns soluble to a developer such as a basesolution after the polymer is reacted with acid. The firstphotosensitive layer 154 further includes a solvent filling inside thepolymer material. The first photosensitive layer 154 includes quencher156 of a first concentration.

The method 130 may proceed to next step 134 by baking the firstphotosensitive layer 154 to reduce the solvent in the firstphotosensitive layer.

The method 130 proceeds to step 136 by forming a second photosensitivelayer 158 on the first photosensitive layer 154, as illustrated in FIG.11 b. The second photosensitive layer 158 utilizes a chemicalamplification (CA) resist material. In one embodiment, a positive CAresist material includes a polymer material that turns soluble to adeveloper such as a base solution after the polymer is reacted withacid. The second photosensitive layer 158 further includes a solventfilling inside the polymer material. The second photosensitive layer 158includes quencher 160 of a second concentration substantially greaterthan the first concentration.

The method 130 may proceed to next step 138 by baking the secondphotosensitive layer 158 to reduce the solvent in the secondphotosensitive layer.

By the two photosensitive layers formed on the substrate in thedisclosed method, the total photosensitive layer (including both thefirst and second photosensitive layers) thus formed presents a gradedquencher distribution along the vertical direction. In one embodiment,the quencher distribution in the total photosensitive layer issubstantially similar to the quencher distribution of the photosensitivelayer 104 in FIG. 2 a. In another embodiment, the graded distribution ofthe quencher is tuned to substantially compensate the optical effect inorder to form an opening with vertical profile.

Two photosensitive layers are formed to achieve graded quencherdistribution. One or more additional photosensitive layers may be formedin a similar way. Each layer has its own quencher concentration. Variousphotosensitive layers and their quencher concentrations are designedsuch that the quencher distribution in the total photosensitive layer istuned to a profile capable of substantially compensating the opticaleffect of the CA resist material during the lithography exposingprocess. In one embodiment, a third photosensitive layer of a thirdconcentration is formed on the second photosensitive layer and the thirdconcentration is greater than the second concentration. A baking processmay be applied to the third photosensitive layer to reduce the solventof the third photosensitive layer. In another embodiment, a fourthphotosensitive layer of a fourth concentration is formed on the thirdphotosensitive layer and the fourth concentration is greater than thethird concentration. A baking process may be followed and applied to thefourth photosensitive layer to reduce the solvent of the fourthphotosensitive layer. All photosensitive layers are collectivelyreferred to as a total photosensitive layer. In one example, the totalphotosensitive layer includes a top portion having a thickness of about25% of the total photosensitive layer; a bottom portion of the totalphotosensitive layer has a thickness of about 25% of the totalphotosensitive layer; the quencher is distributed in the top portionwith a first concentration C1; the quencher is distributed in the bottomportion with a second concentration C2; and the first concentration isgreater than the second concentration. Particularly, (C1-C2)/C2 rangesbetween about 5% and about 30%. In furtherance of the embodiment, thetotal photosensitive layer is formed by four deposition procedures andthe fourth deposited layers have a same thickness. The first layer has afirst concentration R1 and the fourth layer has a fourth concentrationR4. Then the (R4-R1)/R1 ranges between about 5% and about 30%.

The method 130 further proceeds to step 140 by performing an exposingprocess to the total photosensitive layer, resulting in an exposedregion 162 in the total photosensitive layer, as illustrated in FIG. 11c. The method 130 further includes an post-exposure baking (PEB) process142 applied to the total photosensitive layer.

The method 130 proceeds to step 144 to develop the total photosensitivelayer by a developing solution, forming an opening 164 in thephotosensitive layer. In one embodiment, the developing solution isbasic solution. For example, the developing solution is tetramethylammonium hydroxide (TMAH) solution with a proper concentration, such asabout 2.38%. Since the graded quencher concentration is tuned and theoptical effects (explained in FIGS. 1 a˜1 c) are substantiallycompensated. Therefore, the formed opening 164 has a vertical profile,as illustrated in FIG. 11 d. The top rounding and the scumming profileare eliminated or reduced.

FIG. 12 provides a flowchart of a lithography method 165. FIGS. 13 athrough 13 d provide sectional views of a semiconductor device 180fabricated by the method 165 at various lithography patterning steps,constructed according to various aspects of the present disclosure.Referring to FIGS. 12 and 13 a˜13 d, the method 165 and thesemiconductor device 180 are collectively described. The semiconductordevice 180 includes a substrate 182, substantially similar to thesubstrate 102 of FIG. 2.

The method 165 begins at step 166 by forming a first photosensitivelayer 184 on the substrate 182, as illustrated in FIG. 13 a. The firstphotosensitive layer 184 utilizes a chemical amplification (CA) resistmaterial. In one embodiment, a positive CA resist material includes apolymer material that turns soluble to a developer such as a basesolution after the polymer is reacted with acid. The firstphotosensitive layer 184 further includes a solvent filling inside thepolymer material. The first photosensitive layer 184 includes photo-acidgenerator (PAG) 186 of a first concentration.

The method 165 may proceed to next step 168 by baking the firstphotosensitive layer 184 to reduce the solvent in the firstphotosensitive layer.

The method 165 proceeds to step 170 by forming a second photosensitivelayer 188 on the first photosensitive layer 184, as illustrated in FIG.13 b. The second photosensitive layer 188 utilizes a CA resist material.In one embodiment, a positive CA resist material includes a polymermaterial that turns soluble to a developer such as a base solution afterthe polymer is reacted with acid. The second photosensitive layer 188further includes a solvent filling inside the polymer material. Thesecond photosensitive layer 188 includes PAG 190 of a secondconcentration substantially less than the first concentration.

The method 165 may proceed to next step 172 by baking the secondphotosensitive layer 188 to reduce the solvent in the secondphotosensitive layer.

By the two photosensitive layers formed on the substrate in thedisclosed method, the total photosensitive layer (including both thefirst and second photosensitive layers) thus formed presents a gradedPAG distribution along the vertical direction. In one embodiment, thetotal photosensitive layer includes a top portion having a thickness ofabout 25% of the total photosensitive layer; a bottom portion of thetotal photosensitive layer has a thickness of about 25% of the totalphotosensitive layer; the PAG is distributed in the top portion with afirst concentration P1; the PAG is distributed in the bottom portionwith a second concentration P2; and the first concentration is less thanthe second concentration. Particularly, (P2-P1)/P1 ranges between about5% and about 30%. In another embodiment, the graded distribution of thePAG is tuned to substantially compensate the optical effect in order toform an opening with vertical profile.

Two photosensitive layers are formed to achieve graded PAG distribution.One or more additional photosensitive layers may be formed in a similarway. Each layer has its own PAG concentration. Various photosensitivelayers and their PAG concentrations are designed such that the PAGdistribution in the total photosensitive layer is tuned to a profilecapable of substantially compensating the optical effect of the CAresist material during the lithography exposing process. In oneembodiment, a third photosensitive layer having the PAG of a thirdconcentration is formed on the second photosensitive layer and the thirdconcentration is less than the second concentration. A baking processmay be applied to the third photosensitive layer to reduce the solventof the third photosensitive layer. In another embodiment, a fourthphotosensitive layer having PAG of a fourth concentration is formed onthe third photosensitive layer and the fourth concentration is less thanthe third concentration. A baking process may be followed and applied tothe fourth photosensitive layer to reduce the solvent of the fourthphotosensitive layer. All photosensitive layers are collectivelyreferred to as a total photosensitive layer. In one example, the totalphotosensitive layer includes a top portion having a thickness of about25% of the total photosensitive layer; a bottom portion of the totalphotosensitive layer has a thickness of about 25% of the totalphotosensitive layer; the PAG is distributed in the top portion with afirst concentration P1; the PAG is distributed in the bottom portionwith a second concentration P2; and the first concentration is less thanthe second concentration. Particularly, (P2-P1)/P1 ranges between about5% and about 30%. In furtherance of the embodiment, the totalphotosensitive layer is formed by four deposition procedures and thefourth deposited layers have a same thickness. The first layer has afirst concentration R1 and the fourth layer has a fourth concentrationR4. Then the (R4-R1)/R1 ranges between about 5% and about 30%.

The method 165 further proceeds to step 174 by performing an exposingprocess to the total photosensitive layer, resulting in an exposedregion 192 in the total photosensitive layer, as illustrated in FIG. 13c. The method 165 further includes an post-exposure baking (PEB) process176 applied to the total photosensitive layer.

The method 165 proceeds to step 178 to develop the total photosensitivelayer by a developing solution, forming an opening 194 in thephotosensitive layer. In one embodiment, the developing solution isbasic solution. For example, the developing solution is tetramethylammonium hydroxide (TMAH) solution. Since the graded PAG concentrationis tuned and the optical effects are substantially compensated. Forexample, the light absorption leads to less acid generation at thebottom; the less PAG concentration at the top also reduce the acidgenerated there; and the two effects can compensate each other and leadto the uniform acid concentration along the vertical direction.Therefore, the formed opening 194 has a vertical profile, as illustratedin FIG. 13 d. The top rounding and the scumming profile are eliminatedor reduced.

The present disclosure provides various methods and photosensitivematerials for lithography patterning. Other variations in this spiritand scope are considered as consistent with the present disclosure andare suggestive. For example, the lithography patterning methods can beused to pattern one material layer disposed on a semiconductor wafer.This material layer can include silicon, silicon oxide, silicon nitride,titanium nitride, silicon oxynitride, metal oxide (e.g. aluminum oxideor hafnium oxide), metal nitride, metal oxynitride, or siloxane. Anadditional material layer, such as bottom anti-reflective coating(BARC), may be formed on the substrate before forming the photosensitivelayer(s). The photosensitive material can be positive tone oralternatively negative tone. In another embodiment, the photosensitivematerial further includes chromophore, and/or surfactant. Alternatively,a photosensitive material may include photo-base generator. In anotherembodiment, a CA resist includes organic polymer that is acid cleavable.In multilayer photoresist method associated with the method 130 of FIG.10 or the method 165 of FIG. 12, the second photoresist layer has athickness ranging between about 20% and about 500% of the thickness ofthe first photoresist layer.

The foregoing has outlined features of several embodiments so that thoseskilled in the art may better understand the detailed description thatfollows. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions andalterations herein without departing from the spirit and scope of thepresent disclosure.

1. A lithography method, comprising: forming a photosensitive layer on asubstrate, the photosensitive layer including: a polymer that turnssoluble to a base solution in response to reaction with acid; aplurality of photo-acid generators (PAGs) that decompose to form acid inresponse to radiation energy; and a plurality of quenchers havingboiling points distributed between about 200 C. and about 350 C, havingmolecular weights distributed between about 300 Dalton and about 20000Dalton, and vertically distributed in the photosensitive layer such thata first concentration C1 within a top 25% portion of the photosensitivelayer is greater than a second concentration C2 within a bottom 25%portion of the photosensitive layer; exposing the photosensitive layer;baking the photosensitive layer; and developing the exposedphotosensitive layer.
 2. The method of claim 1, wherein (C1-C2)/C2ranges between about 5% and about 30%.
 3. The method of claim 1, whereinthe plurality of quenchers each comprises tri-substitute amine

where Ra, Rb and Rc each includes one of H and an alkyl group and has acarbon number ranging between 6 and
 15. 4. The method of claim 1,wherein each of Ra and Rb further includes a chemical unit selected fromthe group consisting of —Cl; —Br; —I; —NO2; —SO3-; —H—; —CN; —NCO, —OCN;—CO2-; —OH; —OR*, —OC(O)CR*; —SR, —SO2N(R*)2; —SO2R*; SOR; —OC(O)R*;—C(O)OR*; —C(O)R*; —Si(OR*)3; —Si(R*)3; and epoxyl groups, in which R*is selected from the group consisting of H, alkyl group, alkenyl group,and alkynyl groups.
 5. The method of claim 1, wherein the plurality ofquenchers are polymeric quenchers having a structure

where each of R1˜R5 includes one of H, F, alkyl, and fluoroalkyl groupswith carbon number equal or less than 3; each of Ra˜Rd and Rf includes alinking group and includes at least one of the —CO—; —C(═O)O—; —S—; —P—;—P(O2)-; —C(═O)S—; —O—; —N—; —C(═O)N—; —SO2O—; —SO2S—; —SO—, and —SO2-;each of R6˜R11 and Rz includes one of straight, branched, cylclic alky,fluoro alkyl, alkoxyl, and fluoro alkoxyl chain with carbon numberranging from 1 to 15; and x ranges between 1 and
 20. 6. The method ofclaim 5, wherein the polymeric quenchers each has a molecular weightranging between about 1000 Daltons and about 2000 Daltons.
 7. The methodof claim 5, wherein each of R6˜R11 and Rz further includes one of —Cl;—Br; —I; —NO2; —SO3-; —H—; —CN; —NCO, —OCN; —CO2-; —OH; —OR*, —OC(O)CR*;—SR, —SO2N(R*)2; —SO2R*; SOR; —OC(O)R*; —C(O)OR*; —C(O)R*; —Si(OR*)3;—Si(R*)3; and epoxyl group, where R* is selected from the groupconsisting of H, an unbranched, branched, cyclic, noncyclic saturated,unsaturated alkyl, alkenyl, and alkynyl groups.
 8. The method of claim1, wherein the exposing the photosensitive layer is implemented in animmersion lithography apparatus.
 9. A method for a lithography process,comprising: forming a first photosensitive layer on a substrate, thefirst photosensitive layer including a first photo-acid generator (PAG)distributed in the first photosensitive layer and first quenchersdistributed in the first photosensitive layer and having a firstconcentration; forming a second photosensitive layer on the firstphotosensitive layer, the second photosensitive layer including a secondPAG distributed in the second photosensitive layer and second quenchersdistributed in the second photosensitive layer and having a secondconcentration greater than the first concentration; and performing anexposing process to the first and second photosensitive layers.
 10. Themethod of claim 9, wherein the second concentration being greater thanthe first concentration by an amount ranging between about 5% and about30%
 11. The method of claim 9, further comprising: forming a thirdphotosensitive layer on the second photosensitive layer, the thirdphotosensitive layer including a third PAG distributed in the thirdphotosensitive layer and third quenchers distributed in the thirdphotosensitive layer and having a third concentration greater than thesecond concentration, wherein the performing of the exposing processincludes performing the exposing process to the first, second and thirdphotosensitive layer.
 12. The method of claim 9, further comprisingbaking the first and second photosensitive layers, after the performingof the exposing process; and developing the first and secondphotosensitive layers.
 13. The method of claim 9, wherein the first PAGhas a third concentration, the second PAG has a fourth concentrationless than the third concentration.
 14. A method for lithographypatterning, comprising: forming a first photosensitive layer on asubstrate, the first photosensitive layer including a first photo-acidgenerator (PAG) of a first concentration; forming a secondphotosensitive layer on the first photosensitive layer, the secondphotosensitive layer including a second PAG of a second concentrationless than the first concentration; and performing an exposing process tothe first and second photosensitive layers.
 15. The method of claim 14,wherein the first concentration is greater than the second concentrationby an amount ranging between about 5% and about 30%
 16. The method ofclaim 14, further comprising forming a third photosensitive layer on thesecond photosensitive layer, the third photosensitive layer including athird PAG of a third concentration less than the second concentration,wherein the performing of the exposing process includes performing theexposing process to the first, second and third photosensitive layer.17. The method of claim 14, wherein the first photosensitive layerfurther includes a first quencher of a third concentration, the secondphotosensitive layer further includes a second quencher of a fourthconcentration, and the fourth concentration is greater than the thirdconcentration.
 18. A photosensitive material, comprising: a polymer thatturns soluble to a base solution in response to reaction with acid; aplurality of photo-acid generators (PAGs) that decompose to form acid inresponse to radiation energy; and a plurality of quenchers having aboiling point greater than about 300 C.
 19. The material of claim 18,wherein the plurality of quenchers includes molecular weightssubstantially distributed between 1000 Dalton and about 20000 Dalton.20. The material of claim 18, wherein the plurality of quenchers arepolymeric quenchers having a structure

where each of R1˜R5 includes one of H, F, alkyl, and fluoroalkyl groupswith carbon number equal or less than 3; each of Ra˜Rd and Rf includes alinking group and includes at least one of the —CO—; —C(═O)O—; —S—; —P—;—P(O2)-; —C(═O)S—; —O—; —N—; —C(═O)N—; —SO2O—; —SO2S—; —SO—, and —SO2-;each of R6˜R11 and Rz includes one of straight, branched, cylclic alky,fluoro alkyl, alkoxyl, and fluoro alkoxyl chain with carbon numberranging from 1 to 15; and x ranges between 1 and
 20. 21. The material ofclaim 18, wherein each of R6˜R11 and Rz further includes one of —Cl;—Br; —I; —NO2; —SO3-; —H—; —CN; —NCO, —OCN; —CO2-; —OH; —OR*, —OC(O)CR*;—SR, —SO2N(R*)2; —SO2R*; SOR; —OC(O)R*; —C(O)OR*; —C(O)R*; —Si(OR*)3;—Si(R*)3; and epoxyl group, where R* is selected from the groupconsisting of H, an unbranched, branched, cyclic, noncyclic saturated,unsaturated alkyl, alkenyl, and alkynyl groups.